1. Field of the Invention
The present invention relates to a touch-control system, more particularly to an optical touch-control system.
2. Description of the Related Art
U.S. Pat. Nos. 4,507,557 and 5,196,835 disclose conventional optical touch control systems, each of which has a plurality of longitudinal reflecting elements that cooperate to define a rectangular touch-control zone, and a plurality of image acquisition modules and a plurality of light-emitting modules that are disposed at corners of the touch-control zone and oriented toward the touch-control zone, respectively. The reflecting elements serve to reflect light from the light-emitting modules. In such a configuration, each of images captured by the image acquisition modules has a bright band portion, which is attributed to light emitted by the light-emitting modules and light reflected by the reflecting elements. During operation, when a user disposes a pointer (e.g., a finger of the user) in the touch-control zone, light in the touch-control zone is partially obstructed by the pointer such that the bright band portion of each of images captured by the image acquisition modules has a pointer section that is relatively dark and that corresponds in shape to the pointer. Subsequently, position of the pointer relative to the touch-control zone may be determined according to position of pointer the section relative to the bright band portion in each of the images thus captured.
However, when the pointer is disposed too close to one of the image acquisition modules, the pointer may be over-illuminated by light that is emitted by the light-emitting module corresponding to said one of the image acquisition modules, rendering the pointer section of the bright band portion indistinguishable from remaining sections of the bright band portion. As a result, position of the pointer thus determined may be inaccurate. In addition, a shadow of the pointer may also have an adverse influence upon the accuracy of the position of the pointer thus determined due to positional differences among optical axes of the light-emitting modules and the image acquisition modules.
To alleviate the aforesaid drawbacks, U.S. Pat. No. 6,100,538 discloses an optical touch-control system including a plurality of longitudinal light-absorbing elements that cooperate to define a rectangular touch-control zone, and a plurality of image acquisition modules that are oriented toward the touch-control zone, respectively. In such a configuration, each of images captured by the image acquisition modules is plain dark. During operation, when a user disposes a light-emitting pointer in the touch-control zone, each of images captured by the image acquisition modules will have a pointer section that is relatively bright and that corresponds in shape to the pointer. Subsequently, position of the pointer relative to the touch-control zone may be determined according to position of the section pointer in each of the images thus captured. In practice, the pointer may be a stylus that is capable of emitting light through reflection of light from a light source.
However, since the portions of the image corresponding to borders of the touch-control zone may be indistinguishable from remaining portions of the image due to lack of illumination, position of the pointer relative to the touch-control zone thus determined may be inaccurate.
U.S. Pat. No. 7,202,860 discloses an optical touch-control system that is similar to those disclosed in U.S. Pat. Nos. 4,507,557 and 5,196,835. However, the image acquisition modules have a field of view with a border line providing white and black contrast.
When the optical touch-control system is operated in a first mode, a user may dispose a pointer (e.g., a finger of the user) in the touch-control zone to obstruct light in the touch-control zone such that the band portion of each of images captured by the image acquisition modules has a pointer section that is relatively dark and that corresponds in shape to the pointer. The subsequent determination of position of the pointer relative to the touch-control zone is similar to those in U.S. Pat. Nos. 4,507,557 and 5,196,835.
When the optical touch-control system is operated in a second mode, a user may dispose a light-emitting pointer (e.g., the tip of the aforesaid stylus) in the touch-control zone such that the band portion of each of images captured by the image acquisition modules has a pointer section that is relatively bright and that corresponds in shape to the pointer. The subsequent determination of position of the pointer relative to the touch-control zone is similar to that in U.S. Pat. No. 6,100,538.
However, the problem of reduced accuracy of the determined position due to over illumination of the pointer when the pointer is disposed too close to one of the image acquisition modules remains unsolved in the optical touch-control system of U.S. Pat. No. 7,202,860.
Furthermore, for each of the aforesaid optical touch-control systems disclosed in U.S. Pat. Nos. 4,507,557, 5,196,835, and 7,202,860, images captured by each of the image acquisition modules may contain portions corresponding respectively to light emitted by the light-emitting modules that correspond to remaining ones of the image acquisition modules, which may reduce accuracy of the determined position of the pointer. That is to say, for each of the image acquisition modules, the light-emitting modules corresponding to the remaining ones of the image acquisition modules may be regarded as sources of interference.
To solve the aforementioned problem of interference, U.S. Pat. No. 7,232,986 discloses an optical touch-control system wherein, for each of the image acquisition modules to only receive light emitted by the corresponding light-emitting module and to filter light emitted by remaining ones of the light-emitting modules, the image acquisition module must be mounted with an optical filter to block undesired light.
However, optical filters generally have higher production costs and reduce brightness of light that passes therethrough.
In view of the above drawbacks, U.S. Pat. No. 4,144,449 discloses an optical touch-control system that includes a plurality of light-emitting modules that cooperate to define a touch-control zone, and a plurality of image acquisition modules that are disposed respectively at corners of the touch-control zone. Each of the light-emitting modules includes a fluorescent lamp serving as a light-emitting strip, and a pair of structures disposed such that light emitted from the light-emitting strip is directed toward the touch-control zone. Moreover, U.S. Pat. No. 6,972,401 discloses an optical touch-control system similar to that of U.S. Pat. No. 4,144,449. However, in U.S. Pat. No. 6,972,401, each of the light-emitting modules includes a plurality of light-emitting diodes (LEDs) arranged in a longitudinal direction along the light-emitting module, and a diffuser for diffusing light emitted by the LEDs such that light emitted by the LEDs becomes generally continuous illumination.
However, the optical touch-control systems disclosed in U.S. Pat. Nos. 4,144,449 and 6,972,401 have relatively large dimensions and high power consumptions.